This work presents a combined encryption, signature and multisignature scheme with joint security. The motivation lies in a scenario where a personnel in an organisation is required to sign documents individually, and at times involved in a group signing. Our combined scheme attending to the above concerns is based on the joint security notions proposed by Haber and Pinkas, and more recently by Paterson et al, and uses the same key pair for CS-Lite encryption scheme, Okamoto signature scheme and Ma-Weng-Li-Deng multisignature scheme.
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